The present invention relates to a method for repairing a cell having a defect, which is generated during a process for fabricating semiconductor integrated circuits using a laser, and more particularly, to the method for repairing a defect-generated cell using a laser for cutting the defect-generated portion of the cell accurately.
A laser is an optical device providing a monochromatic light having strong directivity, which has been used for the repairing process in the fabricating process of semiconductor devices, since it is possible to focus energy on a minute area.
In other words, the repairing process is a method of cutting a fuse conductive line by controlling the beam energy of the laser, adjusting to the defect-generated portion of the cell for repairing the defect-generated cell. Generally, the fuse conductive line is made up of a polycrystalline silicon layer or polycide line. At this time, it should be noted the the adjacent fuse conductive line, excepting selected one, or substrate can be damaged in the case where the spot size of the laser beam is large or the energy of the laser is excessive.
FIG. 1A is a plan view illustrating alignment of the fuse conductive line and irradiation of the laser beam for repairing, according to a prior art, FIG. 1B is a cross-sectional view illustrating alignment of the fuse conductive line and irradiation of the laser beam for repairing, according to a prior art, FIG. 2A is a plan view of a damaged substrate by high power of the laser, FIG. 2B is a cross-sectional view of a damaged substrate due to the high power of a laser, and FIG. 2C is a plan view illustrating the disconnected state of a fuse conductive line which is not selected due to the misalignment of a laser beam. The prior art will be explained below with reference to the above described figures. In these figures, reference number 1 denotes the fuse conductive line, 2 the laser beam, 3 the gate oxide, 4 the substrate, 5 the isolation layer, 6 the damaged portion of a substrate, 7 the disconnected conductive line and substrate material, and 8 the disconnected portion of the unselected conductive line, respectively.
First, FIG. 1A is a plan view illustrating alignment of the fuse conductive line and irradiation of the laser beam for repairing, according to a prior art, FIG. 1B is a cross-sectional view illustrating alignment of the fuse conductive line and the irradiation of the laser beam for repairing, according to a prior art. Here, the isolation layer 5 is deposited on the fuse conductive line 1, whose deposited thickness is approximately 1 .mu.m. Therefore, the laser used for repairing should have an appropriate energy level which enables the fuse conductive line to be disconnected electrically without doing any damage to the underlayer.
However, the fuse conductive line, having the element isolation layer formed thereon as described above, requires a laser beam with high energy so that it will be difficult to cut the fuse conductive line, and as shown in FIGS. 2A to 2C, results in a disconnection of the fuse conductive line which is not selected and damage of underlying substrate due to no process margin. FIG. 2A is a plan view of a damaged substrate due to the high power of a laser, FIG. 2B is a cross-sectional view of a damaged substrate due to the high power of the laser, and FIG. 2C is a plan view illustrating the disconnected state of the fuse conductive line which is not selected due to misalignment of the laser beam.
Moreover, in the practical repairing process, the adjustment of the energy of the laser beam appropriately is difficult since the disconnection of the fuse conductive line and the damage of the substrate is judged only by discriminating with a naked eye using a microscope.